1. Field of the Invention
This invention relates generally to antenna systems, and more particularly to antennas for use with mobile wireless data collection systems.
2. Description of Related Art
Current “best practices” employed in the movement and tracking of goods in warehouses and distribution centers include the use of barcode-based data collection and wireless networked computers on lift trucks and other mobile material handling equipment. While these technologies have greatly enhanced the efficiency and accuracy of material handling operations over recent decades, they still fundamentally rely on manual data collection activity in the validation of material movement.
For greater efficiencies the data collection needs to be synchronized with operator directives and activity. Operators are typically presented with instructions from the warehouse management software application on the screen of a mobile wireless computer on the lift truck. Upon completion of the required action, the operator typically enters data through a bar code scan or keyboard entry to confirm accurate completion of the task. The information is transmitted over a wireless connection to the application on a network server. The application may then assign the operator the next task. Thus, the application and process require real-time, precise data, appropriate to the task and synchronous with operator actions and application instructions.
Furthermore, almost all full pallet load moves require two basic data collection elements: (1) load identification and (2) location identification. If, for instance, a lift operator is instructed to drive to a particular location, he may then be required to scan a bar code to verify that he has arrived at the correct location. If he is then directed to pick up a pallet, he may then be required to scan a bar code on the pallet load to identify the load to the application software. A subsequent instruction to deposit the load at a particular location would typically be followed by a bar code scan identifying the deposit location to validate task compliance.
The use of radio frequency identification (RFID) technology presents great promise for automating the data collection process. A RFID system typically uses a RFID tag reader to query a RFID tag attached to an object. The RFID tag provides certain information associated with the tagged object. Prior attempts to implement RFID technology in a warehouse environment have typically failed to fully take into account the observations mentioned above.
For example, the use of RFID “portals” at dock doors in warehouses is typically intended to deliver identification of the load passing through the portal and to designate the location (dock door) identification through the reader's network address. However, this is seldom synchronized with lift operator instructions and application instructions to the operator. Also, the attractive characteristic of RFID as a solution approach is that it can be automated easily and does not require “line of sight” to identify items or locations. RFID systems can, and typically do, read multiple tags; but this often results in extraneous data, which fails to deliver discrete, precise data as required by the application. Thus, the use of RFID systems in warehouse inventory control presents a unique set of problems that have to be resolved to ensure efficient operation of the RFID system.
To be successful for use in a warehouse inventory control, the RFID-based solution should address the observations above. A first key will be that the RFID implementation becomes inherently part of the synchronized activities of the lift operation itself. A second key will be that the RFID implementation collects precisely the data expected and required at each step of the lift operation. The RFID tag readers must, therefore, be able to communicate effectively to identify RFID tags, while simultaneously transmitting tag information to a warehouse management system for processing and receiving instructions.
With specific reference to material handling control, the RFID system has to efficiently operate in a harsh operating environment that is typical of a warehouse. RFID tag readers are installed at various locations in the material storage facility. Some of these locations are stationary mounting locations, such as that of a RFID tag reader installed on a post located adjacent to a conveyor belt. Other locations are mobile mounting locations, such as that of a RFID tag reader installed on a lift truck. The RFID tag reader mounted on the lift truck is typically operated to communicate with RFID tags attached to various objects transported by the lift truck as well as stationary objects that may be located on a storage shelf. The results of the tag reads are typically transmitted to the warehouse management system over a wireless local area network.
Mounting the RFID tag reader upon the lift truck involves several operational as well as logistical considerations. Consequently, prior to installation of the RFID tag reader, an acceptable mounting location has to be identified such that installation and operation of the RFID tag reader will not interfere with, nor be affected by, the operation of the forklift. Particularly, antennas for communicating with RFID tags and communicating with the material handling system should be mounted in a manner that addresses multiple factors. Some of these factors include use of low RF power to limit tag readings to a single tag; optimal direction of the RF power pattern to prevent reading unintended tags; rugged construction to withstand typical material handling activities; locating antennas near desired tags to permit use of lower RF power; mounting antennas to limit obstructions to driver visibility; and minimizing cable routing. In other words, RF power control through transmit power level control and RF power distribution through antenna pattern shaping are elements of an effective RFID material handling system.
There remains a need in the industry for a for an antenna system that addresses the aforementioned needs.